Prior art relevant to the present invention and provides the following background information concerning the development of offshore energy systems such as deepwater oil and/or gas production. Long flowlines, power cables, and control umbilicals are frequently required between subsea wells and a host platform. The extended lengths pose energy loss, pressure drop, and production difficulties. The costs of structures for deepwater applications are high and costs frequently increase due to the foreign locations at which they are fabricated.
Other difficulties, associated with deepwater offshore operations, result from floating vessel motions which affect personnel and efficiencies especially when related to liquid dynamics in tanks. The primary motion-related problem, associated with offshore petrochemical operations, occurs with large horizontal vessels in which the liquid level oscillates and provides erroneous signals to the liquid level instruments causing shutdown of processing and overall inefficiency for the operation.
The principal elements which can be modified for improving the motion characteristics of a moored floating vessel are the draft, the water plane area, and its draft rate of change, location of the center of gravity (CG), the metacentric height about which small amplitude roll and pitching motions occur, the frontal area and shape on which winds, current and waves act, the system response of pipe and cables contacting the seabed acting as mooring elements, and the hydrodynamic parameters of added mass and damping. The latter values can be determined by complex solutions of the potential flow equations integrated over the floating vessels detailed features and appendages and then simultaneously solved for the potential source strengths. It is only significant to note herein that the addition of features which allow the added mass and/or damping to be “tuned” for a certain condition requires that several features can be modified in combination, or more preferably independently, to provide the desired properties. The optimization can be greatly simplified if the vessel possesses vertical axial symmetry as in the present invention which reduces the 6 degrees of motion freedom to 4, (i.e. roll=pitch=pendular motion, sway=surge=lateral motion, yaw=rotational motion, and heave=vertical motion). It can be further simplified if hydrodynamic design features can be de-coupled to linearize the process and ease the ideal solution search.
The prior art provides for an offshore floating facility with improved hydrodynamic characteristics and the ability to moor in extended depths thereby providing a satellite platform in deep water resulting in shorter flowline, cables, and umbilicals from the subsea trees to the platform facilities. Previous designs incorporate a retractable center assembly which contains features to enhance the hydrodynamics and allows for the integral use of vertical separators in a quantity and size providing opportunity for individual full time well flow monitoring and extending retention times.
A principal feature of vessels of the industry is a retractable center assembly within the hull, which can be raised or lowered in the field to allow transit in shallow areas. The retractable center assembly provides a means of pitch motion damping, a large volumetric space for the incorporation of optional ballast, storage, vertical pressure or storage vessels, or a centrally located moon pool for deploying diving or remote operated vehicle (ROV) video operations without the need for added support vessels.
Hydrodynamic motion improvements of vessels are provided by: the basic hull configuration; extended skirt and radial fins at the hull base; a (lowered at site) center assembly extending the retractable center section with the base and mid-mounted hydrodynamic skirts and fins, the mass of the separators below the hull deck that lowers the center of gravity; and attachment of the steel catenary risers, cables, umbilicals, and mooring lines near the center of gravity at the hull base. The noted features improve vessel stability and provide increased added mass and damping, which improves the overall response of the system under environmental loading.
Prior art vessels can have hulls which are hexagonal in shape. Floating production, storage and offloading vessel can have an octagonal hull. Prior art floating production, storage, and offloading vessels have a polygonal exterior side wall configuration with sharp corners to cut ice sheets, resist and break ice, and move ice pressure ridges away from the vessel. Prior art also teaches a drilling and production platform consisting of a semi-submersible platform body having the shape of a cylinder having a flat bottom and a circular cross-section. Previous vessels have a peripheral circular cut-out or recess in a lower part of the cylinder, and the design provides a reduction in pitching and rolling movement. Because floating production, storage and offloading vessels may be connected to production risers, and in general the need to be stable, even during storm conditions, remains a need for improvements in vessel hull design.
Further there is a need for improvement in offloading product from a floating production, storage and offloading vessel to a ship or tanker then transporting the product from the floating production, storage and offloading vessel to an onshore facility.
As part of an offloading system, a catenary anchor leg mooring (CALM) buoy, is typically anchored near a floating production, storage and offloading vessel. An example of a buoy usable with the offloading system, the buoy is anchored to the seabed so as to provide a minimum distance from a nearby floating production, storage and offloading vessel. In this example, a pair of cables attaches the buoy to the floating production, storage and offloading vessel and an offloading hose extends from the floating production, storage and offloading vessel to the buoy. A tanker is moored temporarily to the buoy and a hose is extended from the tanker to the buoy for receiving product from the floating production, storage and offloading vessel through hoses connected through the buoy. If adverse weather conditions, such as a storm with significant wind speeds occur during offloading, problems can occur due to movement of the tanker caused by wind and current forces acting on the tanker. Thus, there is also a need for an improvement in the offloading system typically used in transferring product stored on the floating production, storage and offloading vessel to a tanker.
A need exists for a floating vessel that provides kinetic energy absorption capabilities from a watercraft by providing a plurality of dynamic movable tendering mechanisms in a tunnel formed in the floating vessel.
A further need exists for a floating vessel that provides wave damping and wave breakup within a tunnel formed in the floating vessel.
A need exists for a floating vessel that provides friction forces to a hull of a watercraft in the tunnel.
The present embodiments meet these needs.
The present embodiments are detailed below with reference to the listed Figures.